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CAT5e cable Question

Posted on 2007-08-12
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Last Modified: 2011-04-14
Hello,

I have a question regarding CAT5e cabling. I made several CAT5e patch cables. I am aware of the 568a and b standards. My understanding for years has been that it does not matter what standard you use on a patch cable as long as both ends are terminated and crimped in the same order.

Is this correct?
Is there a difference for Gigabit?

Thanks in advance.
Cepolly
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Question by:cepolly
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Expert Comment

by:Rob Williams
ID: 19680511
>>"Is this correct?"
Correct. For the record 568B is more common in the US, and 568A in other countries such as Canada, but it makes no difference. 568A on one end and 568B on the other, and you have a cross-over cable.

>>"Is there a difference for Gigabit?"
Standard is the same for Gigabit, but it uses all 4 pairs. 10/100 only uses 2 pairs, even though all are connected.

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by:cepolly
ID: 19680656
Thanks for the quick response.
Let me clarify.

For example, if I have a cable and I terminate it like this on both ends. will it work?

White/Orange
Orange

White/Green
Green

White/Brown
Brown

White/Blue
Blue

Or do I have to cross Blue and Green?

Thanks.
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by:cepolly
ID: 19680660
...and please remember this is a straight through patch cable
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by:cepolly
ID: 19680669
Sorry I hit submit too fast. Here is the correct reponse:

Thanks for the quick response.
Let me clarify.

For example, if I have a cable and I terminate it like this on both ends. will it work?

White/Orange
Orange

White/Green
Green

White/Blue
Blue

White/Brown
Brown

Or do I have to cross Blue and Green?

Thanks.
0
 
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Accepted Solution

by:
Rob Williams earned 2000 total points
ID: 19680685
No that is not correct.
Have a look at the following link it makes it easy to determine wire positions:
http://www.incentre.net/incentre/frame/ethernet.html
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by:cepolly
ID: 19680716
So just for clarication, I must use the folowing for Gigabit:

White/Orange
Orange

White/Green
Blue

White/Blue
Green

White/Brown
Brown

Thanks
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Expert Comment

by:Rob Williams
ID: 19680723
Correct, if you want to use EIA/TIA 568B. That applies to 10/100 and Gigabit.

If you should want to use 568A (no need) then
White/Green
Green

White/Orange
Blue

White/Blue
Orange

White/Brown
Brown
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by:cepolly
ID: 19680731
Can you explain to me why Pin position makes a difference when both sides are the same and the patch cable is just used for transmission?

For some reason I'm not getting why pin 4 and 6 need to cross. I understand the requirement, just not the reason.

Thanks.
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by:cepolly
ID: 19680742
I think I answered my own question. Tx Rx.
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by:cepolly
ID: 19680762
Actually It's Bi-directional across the board, hence the need for all 4 pair.
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by:cepolly
ID: 19680764
Thanks for the help.
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by:Rob Williams
ID: 19680792
It's due to a couple of factors.
1) the center 4 pins go back to telephone wiring, which for an RJ-45 uses a different standard again, called USOC, but the center 4 pins which the phone uses are the same. Therefore if you wire a jack EIA/TIA 568A/B it can actually be used for network or telephone, depending on what patch cord is used at the patch panel

2) the pairing and twist of the wires is very important. You can wire it anyway you like, so long as pin 1 connects to pin 1 on the other end, however if not done to standard you will introduce in the wire what is called cross talk. The wire will pass a continuity test, and work at 10mbps, but use it for 100mbps and it will fail. The pairing and twist helps to eliminate cross-talk and interference.

It is important to note that making network cables is quite an art. Simply getting a connection, does not guarantee a good cable. Poor terminations, pins rolled over inside by cheap crimpers, kinked or stretched cables, wires with too much twist undone will all reduce performance. If you are making cables they should always be tested and certified, however a tester is over $6000. Best to use factory cables whenever possible.
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by:Rob Williams
ID: 19680797
Thanks cepolly.
Cheers !
--Rob
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by:dannlh
ID: 21656696
It is important to remember that if you are going to pick a standard, you need to stick with that same cabling standard throughout the run of cable including the endpoints and patch cables. This should be noted, because between the A and the B 568 standards as you know the orange and green pairs are swapped. Because these pairs are manufactured at a different twist rate, swapping them between the wall and patch cable could cause an impedance bump in the cabling and affect transmission. e.g. if you use 568A in the wall, and then use 568B patch cables the network will work, but performance could be degraded. You won't normally see this on shorter runs, but on longer runs it can potentially be an issue.

Also you were asking about why the pairs are strangly positioned in the cable. This is because of the pairing for telephone connections. Initally the center pair was used for telephones. As time went on some systems started using the next pair out. This connection was based on the USOC configuation as mentioned above. The EIA/TIA came up with the 568A cabling pinout partially based on this configuration. Unfortunately there was this company AT$T who had a competing standard known as the 256 standard. To be compatible with this wiring the EIA/TIA created the 568B standard with the second and third pairs swapped. The 568B wiring standard is the primary cabling standard in the market.  

Thus your network cables are configured the way they are because of Ma Bell.

To maintain the integrity of your pairs you cannot put your cabling in pair order. e.g. PAIR 1 2 3 4 on pins 1/2 3/4 5/6 7/8. You have to set pair 1 on the center two pins of the 8P8C RJ connector, and pair 2 or 3 straddling that then pair 2 or 3 on pins 1/2 and pair 4 on pins 7/8. ergo EIA/TIA 568B:
 
First color is the insulation, second color is the stripe:
1 wh/or
2 or/wh
3 wh/gr
4 bu/wh
5 wh/bu
6 gr/wh
7 wh/br
8 br/wh

For what its worth, you could swap the wires in a pair e.g. 7 br/wh  8 wh/br if you do the same thing at the other end of that wire. But both ends have to have the same mistake. This kind of swap does not affect the integrity of the wire. It doesn't split the pairs, but it does mess up network people when they look at a cable that is not paired correctly.

If you look at the pinout of an ethernet connector, you will see that it uses pins 1/2 and 3/6 for transmit and receive. They are reversed in a network switch as compared to a workstation. That way you connect transmit to receive and recieve to transmit when you plug in a computer to the switch. When plugging a computer into a computer or a switch to a switch you need a cross-over cable or an uplink port in the switch. This takes care of the swap of transmit and receive for you. Many network switches today can auto-negotiate the transmit an receive pair and swap on the fly.

Finally your question about splitting the pairs. Electrical noise is picked up by wiring. By twisting the pair together and connecting it to a balanced connection (Look at the pinout of your network card again you'll see TX+ and TX- and RX+ and RX-) the system is able to eliminate most of  the noise in the transmission, because both wires will pick up the same noise at approximately the same amplitude. The twisting causes the wires to share approximately the same location in space. Without going into Calculus, basically what happens is the noise cancels itself out on the wires because of the twists. If you don't twist the wires, even with the balanced transmission line, one wire will pick up more noise signal than the other and you won't have the same cancellation.

Does all of this make sense?

dh
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